Synthesis and photocatalytic degradation activities of phosphorus containing ZnO microparticles under visible light irradiation for water treatment applications

Deciphering the Impact of ZnO Nanoparticles and a Sunscreen Product Containing ZnO on Phosphorus Dynamics and Release in Chlorella pyrenoidosa in Aquatic Systems

Zinc oxide nanoparticles (ZnO NPs) expedite the conversion of organic phosphorus (OP) into PO4-P (Pi), facilitating phosphorus (P) absorption by algae. Our study explored the mechanisms of converting OP (2-aminoethylphosphonic acid (AEP) and β-glycerol phosphate (β-GP)) into Pi in Chlorella pyrenoidosa under P deficiency with sunscreen and ZnO NPs. Cell density followed the order of K2HPO4 > β-GP+ZnO > β-GP > AEP+ZnO > AEP > P-free. ZnO NPs promoted the conversion of β-GP, containing C-O-P bonds (0.028-0.041 mg/L), into Pi more efficiently than AEP, which possesses C-P bonds (0.022-0.037 mg/L). Transcriptomics revealed Pi transport/metabolism (phoB (3.99-12.01 fold), phoR (2.20-5.50 fold), ppa (4.49-10.40 fold), and ppk (2.50-5.40 fold)) and phospholipid metabolism (SQD1 (1.85-2.79 fold), SQD2 (2.60-6.53 fold), MGD (2.13-3.21 fold), and DGD (4.08-7.56 fold)) were up-regulated compared to K2HPO4. 31P nuclear magnetic resonance spectroscopy identified intracellular P as polyphosphate, orthophosphate, and pyrophosphate. Synchrotron radiation-based X-ray near-edge structure spectroscopy indicated that K2HPO4 and Zn3(PO4)2 in β-GP+ZnO were increased by 8.09% and 7.28% compared to AEP+ZnO, suggesting superior P storage in β-GP+ZnO. Overall, ZnO NPs improved photoinduced electron-hole pair separation and charge separation efficiency and amplified the ·OH and ·O2- levels, promoting OP photoconversion into Pi and algae growth.

Synergistic effect of Fe doping and oxygen vacancy in AgIO3 for effectively degrading organic pollutants under natural sunlight

In this work, a series of hydrogenated Fe-doped AgIO3 (FAI-x) catalysts are synthesized for photodegrading diverse azo dyes and antibiotics. Under the irradiation of natural sunlight with a light intensity of ∼60 mW/cm2, the optimum FAI-10 exhibits a considerable rate constant for decomposing methyl orange (MO) of 0.067 min-1, about 7.4 times higher than that of AgIO3 (0.009 min-1), and 24.6% and 83.8% of MO can be decomposed over AgIO3 and FAI-10 after irradiation for 40 min. In the amplification photodegradation experiments with using 0.5 g catalyst and 400 mL MO dye solution (10 mg/L), FAI-10 possesses greatly higher photoreactivity to common semiconductors (ZnO, TiO2, In2O3 and Bi2MoO6), and the photodegradation rates over FAI-10 are 92%. Particularly, the FAI-10 shows superior stability, the activity of which remains unaltered after 8 continuous cycles. Foreign ions and water bodies have slight effect on the activity of FAI-10, but the MO degradation rates are decreased by adjusting pH values, especially when pH = 11 because of the strong electrostatic repulsion between MO and FAI-10. FAI-10 can also effectively decompose another azo dye (rhodamine B (RhB)) and diverse antibiotics (sulflsoxazole (SOX), chlortetracycline hydrochloride (CTC), tetracycline hydrochloride (TC) and ofloxacin (OFX)). The activity enhancement mechanism of FAI-10 has been systemically investigated and is ascribed to the promoted photo-absorption, charge separation and transfer efficiency, and affinity of organic pollutants, owing to the synergistic effect of Fe doping and oxygen vacancy (Ov). The photocatalytic mechanisms and process for decomposing MO are verified and proposed based on radical trapping experiments and liquid chromatography-mass spectrometry (LC-MS). This work opens an avenue for the fabrication of effective photocatalysts toward water purification.

S-scheme heterojunctions based on novel Sm2CeMnO6 double perovskite oxide and g-C3N4 with excellent photocatalytic dye degradation performances

It has become of utmost importance to preserve marine life and human health by protecting aquatic environments from contaminants. Therefore, using photocatalytic materials in treatment of contaminated water is a promising and innovative technique. Novel double perovskite Sm2CeMnO6 was synthesized through a modified Pechini sol-gel method. Also, urea and melamine were utilized to synthesize graphitic carbon nitride (g-C3N4). Combination of Sm2CeMnO6 and g-C3N4 produced several S-scheme heterojunction materials in diverse components ratios. Average crystallite sizes of Sm2CeMnO6 and Sm2CeMnO6/g-C3N4 (20:80) samples were calculated by Debye-Scherrer and Williamson-Hall methods to be 19.77, 22.72 nm and 42.01, 43.73 nm, respectively. The coexistence of g-C3N4 (002) with a d-spacing of 0.325 nm and Sm2CeMnO6 planes of (222), (111), and (400) with spacing values of 0.314, 0.302, and 0.294 nm, respectively, was depicted in the HR-TEM image of the Sm2CeMnO6/g-C3N4 (20:80). The estimated bandgaps for the g-C3N4, Sm2CeMnO6, and Sm2CeMnO6/g-C3N4 (20:80) were 2.70, 2.60, and 2.65 eV, respectively. Their application was investigated in photocatalytic degradation of methylene blue (MB) dye as typical pollutant. The estimated degradation pathway of MB was also provided through LC-MS analysis. Under the identical conditions, the best photocatalytic performance was found for Sm2CeMnO6/g-C3N4 (20:80) composite. Using response surface methodology (RSM), operational parameters of the photocatalytic degradation were modeled and optimized by the best composite through central composite design approach. Applying optimized parameters led to 96% degradation of MB (8 mg/L) at pH 10 under 120 min visible light irradiation (λ > 365 nm) using 0.15 g of Sm2CeMnO6/g-C3N4 (20:80) composite in 100 mL aqueous solution. Due to low intrinsic charge transfer resistance, modified Eg, and good performance in e‒/h+ pairs production, Sm2CeMnO6/g-C3N4 (20:80) nanocomposite was introduced as a promising S-scheme photocatalyst.

Novel photo and bio-active greyish-black cotton fabric through air- and nitrogen- carbonized zinc-based MOF for developing durable functional textiles

This study explores the potential of using the carbonization of Zn-based metal-organic frameworks (Zn-MOF-5) under N2 and air to modify zinc oxide (ZnO) nanoparticle for the production of various photo and bio-active greyish-black cotton fabrics. The MOF-derived ZnO under N2 demonstrated a significantly higher specific surface area (259 m2g-1) compared to ZnO (12 m2g-1) and MOF-derived ZnO under air (41.6 m2 g-1). The products were characterized using various techniques, including FTIR, XRD, XPS, FE-SEM, TEM, HRTEM, TGA, DLS, and EDS. The tensile strength and dye degradation properties of the treated fabrics were also investigated. The results indicate that the high dye degradation capability of MOF-derived ZnO under N2 is likely due to the lower ZnO band gap energy and improvement in electron-hole pair stability. Additionally, the antibacterial activities of the treated fabrics against Staphylococcus and Pseudomonas aeruginosa were investigated. The cytotoxicity of the fabrics was studied on human fibroblast cell lines using an MTT assay. The study findings demonstrate that the cotton fabric covered with carbonized Zn-MOF under N2 is human-cell compatible while showing high antibacterial activities and stability against washing, highlighting its potential for use in developing functional textiles with enhanced properties.

Improved cotton fabrics properties using zinc oxide-based nanomaterials: A review

Zinc oxide nanoparticles (ZnO NPs) have gained significant attention in the textile industry for their ability to enhance the physicochemical properties of fabrics. In recent years, there has been a growing focus on the development of ZnO-based nanomaterials and their applications for cotton and other fabrics. This review paper provides an overview of the synthesis and diverse applications of ZnO-based nanomaterials for textile fabrics, including protection against UV irradiation, bacteria, fungi, microwave, electromagnetic radiation, water, and fire. Furthermore, the study offers the potential of these materials in energy harvesting applications, such as wearable pressure sensors, piezoelectric nanogenerators, supercapacitors, and human energy harvesting. Additionally, we discuss the potential of ZnO-based nanomaterials for environmental cleaning, including water, oil, and solid cleaning. The current research in this area has focused on various materials used to prepare ZnO-based nanocomposites, such as metals/nonmetals, semiconductors, metal oxides, carbon materials, polymers, MXene, metal-organic frameworks, and layered double hydroxides. The findings of this review highlight the potential of ZnO-based nanomaterials to improve the performance of textile fabrics in a range of applications, and the importance of continued research in this field to further advance the development and use of ZnO-based nanomaterials in the textile industry.

Shaddock peel-derived N-doped carbon quantum dots coupled with ultrathin BiOBr square nanosheets with boosted visible light response for high-efficiency photodegradation of RhB

In the present work, we constructed a serials of novel shaddock peel-derived N-doped carbon quantum dots (NCQDs) coupled with BiOBr composites. The result showed that the as-synthesized BiOBr (BOB) was composed of ultrathin square nanosheets and flower-like structure, and NCQDs were uniformly dispersed on the surface of BiOBr. Furthermore, the BOB@NCQDs-5 with optimal NCQDs content displayed the top-flight photodegradation efficiency with ca. 99% of removal rate within 20 min under visible light and possessed excellent recyclability and photostability after 5 cycles. The reason was attributed to relatively large BET surface area, the narrow energy gap, inhibited recombination of charge carriers and excellent photoelectrochemical performances. Meanwhile, the improved photodegradation mechanism and possible reaction pathways were also elucidated in detail. On this basis, the study opens a novel perspective to obtain a highly efficient photocatalyst for practical environment remediation.

Delafossite CuCoO2/ZnO derived from ZIF-8 heterojunctions as efficient photoelectrodes for dye-sensitized solar cells

To achieve high-performance dye-sensitized solar cells (DSSCs), it is essential to establish new and effective photoelectrode materials. Herein, we report the successful synthesis of heterojunctions including Cu-based delafossite oxide CuCoO₂ and ZnO derived from zeolitic imidazolate framework-8 (ZIF-8). The layered polyhedral nanocrystals of CuCoO₂ produced through a feasible low temperature hydrothermal process and the faceted nanocrystals of ZnO were achieved by heat treatment of ZIF-8. The composite heterostructures were applied as photoelectrodes in DSSCs assembled using dye N719 and a Pt counter electrode. The physicochemical characteristics (XRD, FESEM, EDAX, mapping, BET, DRS), dye loading, and photovoltaic properties (J-V, EIS, IPCE) of the fabricated materials were studied and fully discussed. Results revealed that addition of CuCoO₂ to ZnO significantly improved the V_oc, J_sc, PCE, FF, and IPCE. Among all cells, CuCoO₂/ZnO (0.1 : 1) showed the best performance (PCE = 6.27%, J_sc = 14.56 mA cm^-2, V_oc = 687.84 mV, FF = 62.67%, IPCE = 45.22%) and acted as a promising photoanode in DSSCs.

Rational modification of TiO2 photoelectrodes with spinel ZnFe2O4 and Ag-doped ZnFe2O4 nanostructures highly enhanced the efficiencies of dye sensitized solar cells

To develop effective photoelectrode nanomaterials for dye-sensitized solar cells (DSSCs), spinel ZnFe₂O₄ (2.5, 5, 7.5, 10 wt%) and Ag-doped ZnFe₂O₄ (Ag_xZn_1-x/2Fe₂O₄, x = 0.1, 0.2, 0.3, 0.4 mmol) nanomaterials were added into the TiO₂ photoanodes. It was found that the DSSC fabricated with TiO₂ + 5 wt% ZnFe₂O₄ exhibited the most improved efficiency of 3.89 % among the ZnFe₂O₄ containing devices. Furthermore, the power conversion efficiency (PCE) values were boosted when the Ag⁺ cations were doped into the ZnFe₂O₄ crystalline lattice. The greatest PCE = 5.75 % was achieved for the solar cell assembled using TiO₂ + 5 wt% Ag_0.2Zn_0.90Fe₂O₄ photoanode indicating 47.81 % improved performance relative to that of the reference DSSC containing TiO₂ + 5 wt% ZnFe₂O₄ photoelectrode. The electrochemical impedance spectra (EIS) approved that the DSSC with the TiO₂ + 5 wt% Ag_0.2Zn_0.90Fe₂O₄ photoelectrode nanomaterial had the lowest charge transfer resistance but the greatest e-h recombination resistance at the interfaces of photoanode/dye/electrolyte. Hence, it had the quickest electron transport rate, and the greatest electron collecting efficiency in addition to the highest dye loading capacity and least photoluminescence (PL) intensity (charge recombination) which were all prominently beneficial for improvement of the DSSC performance.

Photocatalytic degradation of Reactive Black dye using ZnO-CeO2 nanocomposites

This study presents the photocatalytic efficiency of ZnO-CeO₂ nanocomposites for the degradation of a model Reactive Black (RB) dye. Nano-CeO₂ was synthesized using cerium nitrate precursor solution via chemical precipitation. Synthesized nano-CeO₂ was mixed with ZnO nanoparticles in different mass ratios to obtain ZnO-CeO₂ heterojunction photocatalyst. The morphology of the nanocomposites was examined using transmission electron microscope (TEM). X-ray diffraction patterns of the CeO₂ corresponded well with (1 1 1) plane of cubic-phase CeO₂. The band gap of the ZnO-CeO₂ nanocatalyst synthesized was determined to be 3.08 eV, which was lower than that of the pristine CeO₂ and ZnO powders, respectively. The results indicate that 1:1 wt. ratio ZnO-CeO₂ nanocomposite provides about 85% RB degradation within 90 min under UV light under alkaline pH conditions. Degradation rate of RB dye achieved with ZnO-CeO₂ nanocomposite was almost 1.5 times greater than that obtained with pristine ZnO. Increasing CeO₂ ratio beyond 1:1 wt. ratio did not significantly increase RB degradation. The results demonstrate that addition of CeO₂ to ZnO results in lowering its band gap energy and aids charge carrier separation resulting in enhanced oxidation of RB dye under UV light.

Effectively compound the heterojunction formed by flower-like Bi2S3 and g-C3N4 to enhance photocatalytic activity

In this study, the flower-shaped Bi₂S₃/g-C₃N₄-2.6 heterojunction obtained by solvothermal method and its photocatalytic degradation efficiency of rhodamine B (RhB) and tetracycline (TC) in aqueous solution within 40 min is as high as 98.8% and 94.6%. For RhB degradation, the photocatalytic reaction rate constant (k) of Bi₂S₃/g-C₃N₄-2.6 is approximately 1.8 and 45.5 times that of Bi₂S₃ and g-C₃N₄. For TC, k is 3.1 and 2.4 times that of Bi₂S₃ and g-C₃N₄, respectively. The key to determining the high catalytic activity of Bi₂S₃/g-C₃N₄ lies in the formation of a good heterojunction between Bi₂S₃ and g-C₃N₄, which accelerates the electron transfer rate between the heterojunction interface and effectively avoids electron-hole recombination. The effects of catalyst dosage, different pH values, inorganic anions, and capture agents on the photodegradation performance of RhB were investigated. The results show that the catalyst dosage is 1.33 g/L, and the solution pH is in the range of 5-9, which has the best removal effect on pollutants, and the isolation of holes (h⁺) with strong oxidizing ability promotes the collapse of pollutant molecules. Combined with electrochemical tests, a possible degradation mechanism was advised.

Structural engineering of BiOBr nanosheets for boosted photodegradation performance toward rhodamine B

A series of BiOBr nanosheets were synthesized through a facile solvothermal method, whose structures were adjusted by changing solvent ratios. Their photodegradation properties toward rhodamine B (RhB) were further investigated under visible light irradiation. The photocatalytic results indicated that the B-1:3 sample showed superior photoactivity and the RhB removal efficiency attained 97% within 30 min. The outstanding photodegradation activity can be ascribed to the small particle size and thickness, suppressed e--h+ pair recombination and more active electrons and holes. Moreover, free radical quenching experiments suggest that ·O2 - and h+ play a crucial role in improving photoactivity. This work opens a new avenue to boost the removal rate of organic pollutants by engineering the solvent ratios of photocatalysts in the wastewater treatment field.

Highly Efficient Visible Light Active Doped ZnO Photocatalysts for the Treatment of Wastewater Contaminated with Dyes and Pathogens of Emerging Concern

Water is obligatory for sustaining life on Earth. About 71% of the Earth's surface is covered in water. However, only one percent of the total water is drinkable. The presence of contaminants in wastewater, surface water, groundwater, and drinking water is a serious threat to human and environmental health. Their toxic effects and resistance towards conventional water treatment methods have compelled the scientific community to search for an environmentally friendly method that could efficiently degrade toxic contaminants. In this regard, visible light active photocatalysts have proved to be efficient in eliminating a wide variety of water toxins. A plethora of research activities have been carried out and significant amounts of funds are spent on the monitoring and removal of water contaminants, but relatively little attention has been paid to the degradation of persistent water pollutants. In this regard, nanoparticles of doped ZnO are preferred options owing to their low recombination rate and excellent photocatalytic and antimicrobial activity under irradiation of solar light. The current article presents the roles of these nanomaterials for wastewater treatment from pollutants of emerging concern.

An overview on non-spherical semiconductors for heterogeneous photocatalytic degradation of organic water contaminants

Because of their carcinogenicity and mutagenicity, the elimination of organic contaminants from surface and subsurface water is a subject of environmental significance. Conventional water decontamination approaches such as membrane separation, ultrafiltration, adsorption, reverse osmosis, coagulation, etc., have relatively higher operating costs and can generate highly toxic secondary contaminants. On the other hand, heterogeneous photocatalysis, an advanced oxidation process (AOP), is considered a clean and cost-effective process for organic pollutants degradation. Owing to their distinctive structure and physicochemical properties non-spherical semiconductors have gained considerable limelight in the photocatalytic degradation of organic contaminants. The current review briefly introduces a wide range of organic water contaminants. Recent advances in non-spherical semiconductor assembly and their photocatalytic degradation applications are highlighted. The underlying mechanism, fundamentals of photocatalytic reactions, and the factors affecting the degradation performance are also alluded including the current challenges and future research perspectives.

Graphene-Based Materials Immobilized within Chitosan: Applications as Adsorbents for the Removal of Aquatic Pollutants

Graphene and its derivatives, especially graphene oxide (GO), are attracting considerable interest in the fabrication of new adsorbents that have the potential to remove various pollutants that have escaped into the aquatic environment. Herein, the development of GO/chitosan (GO/CS) composites as adsorbent materials is described and reviewed. This combination is interesting as the addition of graphene to chitosan enhances its mechanical properties, while the chitosan hydrogel serves as an immobilization matrix for graphene. Following a brief description of both graphene and chitosan as independent adsorbent materials, the emerging GO/CS composites are introduced. The additional materials that have been added to the GO/CS composites, including magnetic iron oxides, chelating agents, cyclodextrins, additional adsorbents and polymeric blends, are then described and discussed. The performance of these materials in the removal of heavy metal ions, dyes and other organic molecules are discussed followed by the introduction of strategies employed in the regeneration of the GO/CS adsorbents. It is clear that, while some challenges exist, including cost, regeneration and selectivity in the adsorption process, the GO/CS composites are emerging as promising adsorbent materials.

A facile synthesis of nano AgBr attached potato-like Ag2MoO4 composite as highly visible-light active photocatalyst for purification of industrial waste-water

In recent times, silver (Ag) based semiconductors have been gained a lot of attention as photocatalysts for industrial waste-water treatment owing to their strong visible-light absorbing capability and small bandgap energy. Therefore, herein, we have designed and utilized a one-pot hydrothermal approach to the synthesis of nano-sized AgBr covered potato-like Ag₂MoO₄ composite photocatalysts for the elimination of organic wastes from the aquatic environment. To achieve a high-performance photocatalyst, a sequence of AgBr/Ag₂MoO₄ composites were acquired with varying CTAB from 1 to 4 mmol. Furthermore, the photocatalytic activity of these photocatalysts was confirmed from decomposing of Rhodamine B (RhB) dye via visible-light elucidation. It can be noticed that AgBr/Ag₂MoO₄ composites exhibited significantly increased photocatalytic behaviour as compared with pure AgBr and Ag₂MoO₄. Surprisingly, the AgBr/Ag₂MoO₄ composite obtained from 2 mmol CTAB was eliminated the entire RhB dye with 25 min. Also, the recycling experiment indicates the AgBr/Ag₂MoO₄ composite has an excellent photo-stability. Accordingly, the as-acquired AgBr/Ag₂MoO₄ composite would be a suitable photocatalytic material for industrial waste-water purification.

Exfoliated Clay Decorated with Magnetic Iron Nanoparticles for Crystal Violet Adsorption: Modeling and Physicochemical Interpretation

Surfactant–modified exfoliated Fayum clay (CTAB–EC) obtained after chemical treatment with a CTAB/H₂O₂ solution was further decorated with magnetic Fe₃O₄ nanoparticles (MNP). The final nanocomposite (MNP/CTAB–EC) was characterized by XRD, SEM, FTIR, TEM and its adsorptive capability against a model cationic dye, crystal violet (CV), was evaluated. A comparison of the adsorption performance of the raw clay and its modified counterparts using H₂O₂, CTAB, CTAB/H₂O₂ or MNP indicated that the adsorption capacity of MNP/CTAB–EC was the highest for CV removal at pH 8.0. The pseudo‒second order for the kinetics and Freundlich model for adsorption equilibrium fitted well the CV removal experimental data at all tested temperatures (25, 40 and 55 °C). The enhancement of the Langmuir adsorption capacity from 447.1 to 499.4 mg g⁻¹ with increasing the temperature from 25 to 55 °C revealed an endothermic nature of the removal process. The interactions between CV and MNP/CTAB–EC were interpreted using advanced statistical physics models (ASPM) in order to elucidate the adsorption mechanism. Multilayer model fitted the adsorption process and therefore, the steric and energetic factors that impacted the CV adsorption were also interpreted using this model. The aggregated number of CV molecules per MNP/CTAB–EC active site (n) was more than unity at all temperatures, representing thus a vertical adsorption orientation and a multi‒interactions mechanism. It was determined that the increase of CV uptake with temperature was mainly controlled by the increase of the number of active sites (N_M). Calculated adsorption energies (ΔE) revealed that CV removal was an endothermic and a physisorption process (ΔE < 40 kJ mol ⁻¹). MNP/CTAB–EC was magnetically separated, regenerated by NaOH, and reused without significant decrease in its adsorption efficiency, supporting a prosperity of its utilization as an effective adsorbent against hazardous dyes from wastewaters.

A Novel Nanocomposite of Activated Serpentine Mineral Decorated with Magnetic Nanoparticles for Rapid and Effective Adsorption of Hazardous Cationic Dyes: Kinetics and Equilibrium Studies

A widely distributed mineral, serpentine, obtained from Wadi Ghadir (Eastern Desert in Egypt) was studied as a potential naturally and abundantly available source for the synthesis of an efficient adsorbent for aquatic remediation applications. A novel nanocomposite was synthesized after the exfoliation of the layered structure of serpentine by hydrogen peroxide treatment (serpentine (SP)), followed by decoration with magnetic Fe3O4 nanoparticles (MNP). The goal behind the utilization of the latter phase was to increase the environmental remediation capability and to incorporate magnetic properties at the final adsorbent, toward a better separation after the use. The fabricated composite (MNP/SP) was characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM). The composite's potential adsorption application toward the removal of two cationic dyes, methylene blue (MB) and malachite green (MG), was investigated. The observed adsorption kinetics was fast, and the highest uptake was observed at pH = 8, with the capacities to reach 162 and 176 mg g-1 for MB and MG, respectively, values significantly higher than various other materials tested against these two cationic dyes. Compared to hydrogen peroxide-treated serpentine, the removal efficiency of the composite was higher by 157 and 127% for MB and MG, respectively. The MB and MG were adsorbed because of the favorable electrostatic interactions between MNP/SP active sites and the cationic dyes. The close value capacities suggest that the difference in chemistry of the two dyes does not affect the interactions, with the later occurring via the dyes' amine functionalities. With increasing ionic strength, the adsorption of the studied basic dyes was slightly decreased, suggesting only partial antagonistic ion effect. The sorbent can be easily regenerated and reused without significant deterioration of its adsorption efficiency, which makes MNP/SP a promising adsorbent for the removal of hazardous pollutants from aquatic environments.